I think you'll find it's simple physics. You been used to mounting some heavy lenses on your camera. When you lift that amount of size and weight you have to make a certain effort. By contrast the 35 f2 IS is relatively small and light so you use much less effort to handle it. Because you're mounting less mass it feels much tighter. This is also why people report the 40 pancake to be tight compared with other lenses. If the EF mount was so tight that a large lens like the 70-200/2.8 felt tight the 40 pancake would be an enormous effort !
(I assume your 50 f1.8 has a plastic bayonet mount which is why it will feel soft).
Thats true... makes sense. Although the 24-70 f4 IS is about the same size and weight (maybe just slightly more) and it didnt feel much different. I've also mounted a 24-105 f4 IS and a few other metal mount lenses like the tokina 11-16 on my crop body. All of those are heavier than the new 35 but still not even close to the 85 or 70-200.
Since yesterday, it seems to be a little less tight. I was just uncomfortable about it for a minute since it's probably the first lens I bought online that was NOT from B&H.
Try freezing your lens before mounting it, that will shrink the metal and give it more tolerance. Of course the mount may seize up when the metals of the lens and the camera mount reach the same temperature
I'll do that right after I grind the threads off, then ill apply some lube to assure no extra friction, for good measure X)